The present invention relates to a focusing detection device which uses circuits with unexceptional high frequency characteristics and yet is able to detect the optimum focusing position with improved accuracy.
A conventional focusing detection device is known wherein an array of photoelectric elements, such as photodiodes, are used which share a small light receiving area on the imaging surface of a lens (for example, the film surface of a camera) or an equivalent surface (a glass surface for focusing the viewfinder of a camera). In such a device, the photoelectric elements are sequentially driven by clock pulses from a clock pulse generating device so as to sequentially provide outputs according to the image. Since it is known that focusing is accomplished when the output from the photoelectric elements is maximized, this output is differentiated to obtain the maximum value of the output of the photoelectric elements. The differentiated output is rectified and the signal of the same symbol is integrated, and the integrated value is displayed on a meter. When the meter shows the maximum value, the optical system involved is in the position for optimum focusing.
In a conventional circuit as constructed above, a very high frequency component is included when the signal is built up. Thus, a circuit with good frequency characteristics, even in a higher range, is required as a signal processing circuit. Further, since the circuit for differentiating the output from the photoelectric elements and for obtaining the extreme values is performing analog processing, this device is defective in that, although the operation speed is fast, the accuracy is not too good.